NSBundle

An NSBundle object represents a location in the file system that groups code and resources that can be used in a program. NSBundle objects locate program resources, dynamically load and unload executable code, and assist in localization. You build a bundle in Xcode using one of these project types: Application, Framework, plug-ins.

Although bundle structures vary depending on the target platform and the type of bundle you are building, the NSBundle class hides this underlying structure in most (but not all) cases. Many of the methods you use to load resources from a bundle automatically locate the appropriate starting directory and look for resources in known places. For information about application bundle structures (for OS X and iOS), see Bundle Programming Guide. For information about the structure of framework bundles, see Framework Programming Guide. For information about the structure of OS X plug-ins, see Code Loading Programming Topics.

For additional information about how to load nib files and images in a Mac app, see NSBundle AppKit Additions Reference. For information about how to load nib files in an iOS application, see NSBundle UIKit Additions Reference.

Unlike some other Foundation classes with corresponding Core Foundation names (such as NSString and CFString), NSBundle objects cannot be cast (“toll-free bridged”) to CFBundle references. If you need functionality provided in CFBundle, you can still create a CFBundle and use the CFBundle Reference API. See Interchangeable Data Types for more information on toll-free bridging.

Declaration

Parameters

url

The file URL to a directory. This must be a full URL for a directory; if it contains any symbolic links, they must be resolvable.

Return Value

An NSBundle object initialized to correspond to url. This method initializes and returns a new instance only if there is no existing bundle associated with url, otherwise it deallocates self and returns the existing object. If url doesn’t exist or the user doesn’t have access to it, returns nil.

Discussion

It’s not necessary to allocate and initialize an instance for the main bundle; use the mainBundle class method to get this instance. You can also use the bundleWithURL: class method to obtain a bundle identified by its file URL.

Declaration

Parameters

fullPath

The path to a directory. This must be a full pathname for a directory; if it contains any symbolic links, they must be resolvable.

Return Value

An NSBundle object initialized to correspond to fullPath. This method initializes and returns a new instance only if there is no existing bundle associated with fullPath, otherwise it deallocates self and returns the existing object. If fullPath doesn’t exist or the user doesn’t have access to it, returns nil.

Discussion

It’s not necessary to allocate and initialize an instance for the main bundle; use the mainBundle class method to get this instance. You can also use the bundleWithPath: class method to obtain a bundle identified by its directory path.

Import Statement

Availability

See Also

Returns the NSBundle object with which the specified class is associated.

Declaration

Swift

init(forClassaClass: AnyClass) -> NSBundle

Objective-C

+ (NSBundle *)bundleForClass:(Class)aClass

Parameters

aClass

A class.

Return Value

The NSBundle object that dynamically loaded aClass (a loadable bundle), the NSBundle object for the framework in which aClass is defined, or the main bundle object if aClass was not dynamically loaded or is not defined in a framework.

Declaration

Parameters

Return Value

The previously created NSBundle instance that has the bundle identifier identifier. Returns nil if the requested bundle is not found.

Discussion

This method is typically used by frameworks and plug-ins to locate their own bundle at runtime. This method may be somewhat more efficient than trying to locate the bundle using the bundleForClass: method. However, if the initial lookup of an already loaded and cached bundle with the specified identifier fails, this method uses potentially time-consuming heuristics to attempt to locate the bundle.

Declaration

Return Value

The NSBundle object that corresponds to the directory where the application executable is located, or nil if a bundle object could not be created.

Discussion

This method allocates and initializes a bundle object if one doesn’t already exist. The new object corresponds to the directory where the application executable is located. Be sure to check the return value to make sure you have a valid bundle. This method may return a valid bundle object even for unbundled applications.

In general, the main bundle corresponds to an application file package or application wrapper: a directory that bears the name of the application and is marked by a “.app” extension.

Declaration

Parameters

Return Value

The Class object for className. Returns nil if className is not one of the classes associated with the receiver or if there is an error loading the executable code containing the class implementation.

Discussion

If the bundle’s executable code is not yet loaded, this method dynamically loads it into memory. Classes (and categories) are loaded from just one file within the bundle directory; this code file has the same name as the directory, but without the extension (“.bundle”, “.app”, “.framework”). As a side effect of code loading, the receiver posts NSBundleDidLoadNotification after all classes and categories have been loaded; see Notifications for details.

Import Statement

Availability

See Also

Declaration

Swift

var principalClass: AnyClass? { get }

Objective-C

@property(readonly)ClassprincipalClass

Discussion

This property is set after ensuring that the code containing the definition of the class is dynamically loaded. If the bundle encounters errors in loading or if it can’t find the executable code file in the bundle directory, this property is nil.

The principal class typically controls all the other classes in the bundle; it should mediate between those classes and classes external to the bundle. Classes (and categories) are loaded from just one file within the bundle directory. The bundle obtains the name of the code file to load from the dictionary returned from infoDictionary, using “NSExecutable” as the key. The bundle determines its principal class in one of two ways:

It first looks in its own information dictionary, which extracts the information encoded in the bundle’s property list (Info.plist). The bundle obtains the principal class from the dictionary using the key NSPrincipalClass. For non-loadable bundles (applications and frameworks), if the principal class is not specified in the property list, this property is nil.

If the principal class is not specified in the information dictionary, the bundle identifies the first class loaded as the principal class. When several classes are linked into a dynamically loadable file, the default principal class is the first one listed on the ld command line. In the following example, Reporter would be the principal class:

ld-omyBundle-rReporter.oNotePad.oQueryList.o

The order of classes in Xcode’s project browser is the order in which they will be linked. To designate the principal class, control-drag the file containing its implementation to the top of the list.

The following method obtains a bundle by specifying its path (bundleWithPath:), then loads the bundle with principalClass and uses the principal class object to allocate and initialize an instance of that class:

Parameters

The name of a resource file contained in the directory specified by bundleURL.

extension

If extension is an empty string or nil, the extension is assumed not to exist and the file URL is the first file encountered that exactly matches name.

subpath

The path of a top-level bundle directory. This must be a valid path. For example, to specify the bundle directory for a Mac app, you might specify the path /Applications/MyApp.app.

Return Value

The file URL for the resource file or nil if the file could not be located. This method also returns nil if the bundle specified by the bundlePath parameter does not exist or is not a readable directory.

Parameters

The name of a resource file contained in the directory specified by bundlePath.

extension

If extension is an empty string or nil, the extension is assumed not to exist and the file is the first file encountered that exactly matches name.

bundlePath

The path of a top-level bundle directory. This must be a valid path. For example, to specify the bundle directory for a Mac app, you might specify the path /Applications/MyApp.app.

Return Value

The full pathname for the resource file or nil if the file could not be located. This method also returns nil if the bundle specified by the bundlePath parameter does not exist or is not a readable directory.

Discussion

This method is best suited only for the occasional retrieval of resource files. In most cases where you need to retrieve bundle resources, it is preferable to use the NSBundle instance methods instead.

Declaration

Parameters

The name of the resource file. If name is an empty string or nil, returns the first file encountered of the supplied type.

extension

If extension is an empty string or nil, the extension is assumed not to exist and the file is the first file encountered that exactly matches name.

Return Value

The full pathname for the resource file or nil if the file could not be located.

Discussion

The method first looks for a matching resource file in the non-localized resource directory of the specified bundle. If a matching resource file is not found, it then looks in the top level of an available language-specific .lproj folder. (The search order for the language-specific folders corresponds to the user’s preferences.) It does not recurse through other subfolders at any of these locations. For more details on how localized resources are found, read The Bundle Search Pattern in Bundle Programming Guide.

The following code fragment gets the path to a plist within the bundle, and loads it into an NSDictionary.

Parameters

Return Value

An array of file URLs for the resource files or nil if no files could be located at subpath with extension. Returns an empty array if no matching resource files are found.

Discussion

If subpath is nil, this method searches the top-level non-localized resource directory and the top-level of any language-specific directories. (In OS X, the top-level non-localized resource directory is typically called Resources but in iOS, it is the main bundle directory.)

For example, suppose you have a Mac app with a modern bundle and you specify @"Documentation" for the subpath parameter. This method would first look in the Contents/Resources/Documentation directory of the bundle, followed by the Documentation subdirectories of each language-specific .lproj directory. (The search order for the language-specific directories corresponds to the user’s preferences.) This method does not recurse through any other subdirectories at any of these locations. For more details see The Bundle Search Pattern in Bundle Programming Guide.

Parameters

If extension is an empty string or nil, all the files in subpath and its subdirectories are returned. If an extension is provided the subdirectories are not searched.

subpath

The name of the bundle subdirectory. Can be nil.

Return Value

An array of full pathnames for the subpath or nil if no files are located.

Discussion

If subpath is nil, this method searches the top-level nonlocalized resource directory and the top-level of any language-specific directories. (In OS X, the top-level nonlocalized resource directory is typically called Resources but in iOS, it is the main bundle directory.) For example, suppose you have a Mac app with a modern bundle and you specify @"Documentation" for the subpath parameter. This method would first look in the Contents/Resources/Documentation directory of the bundle, followed by the Documentation subdirectories of each language-specific .lproj directory.

Whether this method recurses through subdirectories is dependent on the extension parameter. If nil or an empty string it will recurse, otherwise, it does not. (The search order for the language-specific directories corresponds to the user’s preferences.) For details on how localized resources are found, read The Bundle Search Pattern in Bundle Programming Guide.

Returns the file URL for the resource identified by the specified name and file extension, located in the specified bundle subdirectory, and limited to global resources and those associated with the specified localization.

Availability

Returns the full pathname for the resource identified by the specified name and file extension, located in the specified bundle subdirectory, and limited to global resources and those associated with the specified localization.

Parameters

If extension is an empty string or nil, the extension is assumed not to exist and the file is the first file encountered that exactly matches name.

subpath

The name of the bundle subdirectory to search.

localizationName

The language ID for of the localization. This parameter should correspond to the name of one of the bundle's language-specific resource directories without the .lproj extension.

Return Value

The full pathname for the resource file or nil if the file could not be located.

Discussion

This method is equivalent to pathForResource:ofType:inDirectory:, except that only nonlocalized resources and those in the language-specific .lproj directory specified by localizationName are searched.

Parameters

The file extension. If extension is an empty string or nil, the extension is assumed not to exist, all the files in bundlePath are returned.

bundlePath

The top-level directory of a bundle. This must represent a valid path.

Return Value

An array containing the full pathnames for all bundle resources with the specified extension. This method returns an empty array if no matching resource files are found. It also returns an empty array if the bundle specified by the bundlePath parameter does not exist or is not a readable directory.

This method is best suited only for the occasional retrieval of resource files. In most cases where you need to retrieve bundle resources, it is preferable to use the NSBundle instance methods instead.

Parameters

The file extension. If extension is an empty string or nil, the extension is assumed not to exist, all the files in subpath are returned.

subpath

The name of the bundle subdirectory to search.

Return Value

An array containing the full pathnames for all bundle resources matching the specified criteria. This method returns an empty array if no matching resource files are found.

Discussion

This method provides a means for dynamically discovering multiple bundle resources of the same type. If extension is an empty string or nil, all bundle resources in the specified resource directory are returned.

The argument subpath specifies the name of a specific subdirectory to search within the current bundle’s resource directory hierarchy. If subpath is nil, this method searches the top-level nonlocalized resource directory and the top-level of any language-specific directories. (In OS X, the top-level nonlocalized resource directory is typically called Resources but in iOS, it is the main bundle directory.) For example, suppose you have a Mac app with a modern bundle and you specify @"Documentation" for the subpath parameter. This method would first look in the Contents/Resources/Documentation directory of the bundle, followed by the Documentation subdirectories of each language-specific .lproj directory. (The search order for the language-specific directories corresponds to the user’s preferences.) This method does not recurse through any other subdirectories at any of these locations. For details on how localized resources are found, read The Bundle Search Pattern in Bundle Programming Guide.

Returns an array containing the file URLs for all bundle resources having the specified filename extension, residing in the specified resource subdirectory, and limited to global resources and those associated with the specified localization.

Availability

Returns an array containing the file for all bundle resources having the specified filename extension, residing in the specified resource subdirectory, and limited to global resources and those associated with the specified localization.

Parameters

The language ID for the localization. This parameter should correspond to the name of one of the bundle's language-specific resource directories without the .lproj extension.

Return Value

An array containing the full pathnames for all bundle resources matching the specified criteria. This method returns an empty array if no matching resource files are found.

Discussion

This method is equivalent to pathsForResourcesOfType:inDirectory:, except that only nonlocalized resources and those in the language-specific .lproj directory specified by localizationName are searched.

Declaration

Discussion

For an application purchased from the App Store, use this application bundle property to locate the receipt. This property makes no guarantee about whether there is a file at the URL—only that if a receipt is present, that is its location.

Note

The general best practice of weak linking using the respondsToSelector: method cannot be used here. Prior to iOS 7, the method was implemented as private SPI, but that implementation called the doesNotRecognizeSelector: method.

Declaration

Discussion

If the bundle does not contain an Info.plist file, this dictionary contains only private keys that are used internally by the NSBundle class. The NSBundle class may add extra keys to this dictionary for its own use. Common keys for accessing the values of the dictionary are CFBundleIdentifier, NSMainNibFile, and NSPrincipalClass.

Parameters

The value to return if key is nil or if a localized string for key can’t be found in the table.

tableName

The receiver’s string table to search. If tableName is nil or is an empty string, the method attempts to use the table in Localizable.strings.

Return Value

A localized version of the string designated by key in table tableName. This method returns the following when key is nil or not found in table:

If key is nil and value is nil, returns an empty string.

If key is nil and value is non-nil, returns value.

If key is not found and value is nil or an empty string, returns key.

If key is not found and value is non-nil and not empty, return value.

Discussion

For more details about string localization and the specification of a .strings file, see “String Resources.”

Using the user default NSShowNonLocalizedStrings, you can alter the behavior of localizedStringForKey:value:table: to log a message when the method can’t find a localized string. If you set this default to YEStrue (in the global domain or in the application’s domain), then when the method can’t find a localized string in the table, it logs a message to the console and capitalizes key before returning it.

The following example cycles through a static array of keys when a button is clicked, gets the value for each key from a strings table named Buttons.strings, and sets the button title with the returned value:

Declaration

Discussion

An array of NSNumber objects, each of which contains an integer value corresponding to a supported processor architecture. For a list of common architecture types, see the constants in Mach-O Architecture. If the bundle does not contain a Mach-O executable, this is nil.

The bundle scans its Mach-O executable and returns all of the architecture types it finds. Because they are taken directly from the executable, the values may not always correspond to one of the well-known CPU types defined in Mach-O Architecture.

Declaration

Parameters

error

On input, a pointer to an error object variable. On output, this variable may contain an error object indicating why the bundle’s executable could not be loaded. If no error would occur, this parameter is left unmodified. You may specify nil for this parameter if you are not interested in the error information.

Return Value

YEStrue if the bundle’s executable code could be loaded successfully or is already loaded; otherwise, NOfalse if the code could not be loaded.

Discussion

This method does not actually load the bundle’s executable code. Instead, it performs several checks to see if the code could be loaded and with one exception returns the same errors that would occur during an actual load operation. The one exception is the NSExecutableLinkError error, which requires the actual loading of the code to verify link errors.

Import Statement

Availability

See Also

Dynamically loads the bundle’s executable code into a running program, if the code has not already been loaded.

Declaration

Swift

funcload() -> Bool

Objective-C

- (BOOL)load

Return Value

YEStrue if the method successfully loads the bundle’s code or if the code has already been loaded, otherwise NOfalse.

Discussion

You can use this method to load the code associated with a dynamically loaded bundle, such as a plug-in or framework. Prior to OS X version 10.5, a bundle would attempt to load its code—if it had any—only once. Once loaded, you could not unload that code. In OS X version 10.5 and later, you can unload a bundle’s executable code using the unload method.

You don’t need to load a bundle’s executable code to search the bundle’s resources.

This method initializes the principal class in the bundle. Therefore, to add code you want executed after loading, override the initialize class method of the principal class.

Declaration

Parameters

error

On input, a pointer to an error object variable. On output, this variable may contain an error object indicating why the bundle’s executable could not be loaded. If no error occurred, this parameter is left unmodified. You may specify nil for this parameter if you are not interested in the error information.

Return Value

YEStrue if the bundle’s executable code was loaded successfully or was already loaded; otherwise, NOfalse if the code could not be loaded.

Discussion

If this method returns NOfalse and you pass a value for the error parameter, a suitable error object is returned in that parameter. Potential errors returned are in the Cocoa error domain and include the types that follow. For a full list of error types, see FoundationErrors.h.

NSFileNoSuchFileError - returned if the bundle’s executable file was not located.

NSExecutableNotLoadableError - returned if the bundle’s executable file exists but could not be loaded. This error is returned if the executable is not recognized as a loadable executable. It can also be returned if the executable is a PEF/CFM executable but the current process does not support that type of executable.

NSExecutableArchitectureMismatchError - returned if the bundle executable does not include code that matches the processor architecture of the current processor.

NSExecutableRuntimeMismatchError - returned if the bundle’s required Objective-C runtime information is not compatible with the runtime of the current process.

NSExecutableLoadError - returned if the bundle’s executable failed to load for some detectable reason prior to linking. This error might occur if the bundle depends on a framework or library that is missing or if the required framework or library is not compatible with the current architecture or runtime version.

NSExecutableLinkError - returned if the executable failed to load due to link errors but is otherwise alright.

The error object may contain additional debugging information in its description that you can use to identify the cause of the error. (This debugging information should not be displayed to the user.) You can obtain the debugging information by invoking the error object’s description method in your code or by using the print-object command on the error object in gdb.

Availability

See Also

Declaration

Return Value

YEStrue if the bundle was successfully unloaded or was not already loaded; otherwise, NOfalse if the bundle could not be unloaded.

Discussion

This method attempts to unload a bundle’s executable code using the underlying dynamic loader (typically dyld). You may use this method to unload plug-in and framework bundles when you no longer need the code they contain. You should use this method to unload bundles that were loaded using the methods of the NSBundle class only. Do not use this method to unload bundles that were originally loaded using the bundle-manipulation functions in Core Foundation.

It is the responsibility of the caller to ensure that no in-memory objects or data structures refer to the code being unloaded. For example, if you have an object whose class is defined in a bundle, you must release that object prior to unloading the bundle. Similarly, your code should not attempt to access any symbols defined in an unloaded bundle.

Special Considerations

Prior to OS X version 10.5, code could not be unloaded once loaded, and this method would always return NOfalse. In OS X version 10.5 and later, you can unload a bundle’s executable code using this method.

Declaration

Parameters

localizationsArray

An array of NSString objects, each of which specifies the language ID for a localization that the bundle supports.

Return Value

An array of NSString objects containing the preferred localizations. These strings are ordered in the array according to the user's language preferences and are taken from the strings in the localizationsArray parameter.

Discussion

This method does not return all localizations in preference order but only those from which NSBundle would get localized content, typically either a single non-region-specific localization or a region-specific localization followed by a corresponding non-region-specific localization as a fallback.

However, clients who want all localizations in preference order can make repeated calls, each time taking the top localizations out of the list of localizations passed in.

Parameters

An array of NSString objects, each of which specifies the language ID for a localization that the bundle supports.

preferencesArray

An array of NSString objects containing the user's preferred localizations. If this parameter is nil, the method uses the user's localization preferences.

Return Value

An array of NSString objects, each of which identifies a localization in the receiver’s bundle. These strings are ordered in the array according to the specified preferences and are taken from the strings in the localizationsArray parameter. If none of the user-preferred localizations are available in the bundle, this method returns one of the bundle localizations.

Discussion

This method does not return all localizations in preference order but only those from which NSBundle would get localized content, typically either a single non-region-specific localization or a region-specific localization followed by a corresponding non-region-specific localization as a fallback.

However, clients who want all localizations in preference order can make repeated calls, each time taking the top localizations out of the list of localizations passed in.

Declaration

Discussion

This property uses the preferred localization for the current user when determining which resources to include. If the preferred localization is not available, this property chooses the most appropriate localization found in the bundle.

NSBundle posts NSBundleDidLoadNotification to notify observers which classes and categories have been dynamically loaded. When a request is made to an NSBundle object for a class (classNamed: or principalClass), the bundle dynamically loads the executable code file that contains the class implementation and all other class definitions contained in the file. After the module is loaded, the bundle posts the NSBundleDidLoadNotification.

The notification object is the NSBundle instance that dynamically loads classes. The userInfo dictionary contains an NSLoadedClasses key.

In a typical use of this notification, an object might want to enumerate the userInfo array to check if each loaded class conformed to a certain protocol (say, an protocol for a plug-and-play tool set); if a class does conform, the object would create an instance of that class and add the instance to another NSArray object.